A client device as defined in the present disclosure is a device that may access voice, video, text, instant messaging, internet and other services from a number of sources including wireless communication networks, Wi-Fi, Ethernet, etc. Such client devices may include conventional devices such as a smartphone, a tablet, a feature-phone, a laptop, etc. Other client devices may include devices that are embedded within devices that perform other functions such as an entertainment system in a home or in an automobile, a home appliance such as a refrigerator or washer/dryer, a wristwatch with a heart rate monitor, a medical device such as a blood pressure meter or insulin sensor, a utility meter, a gaming console, a camera, a navigation device, an industrial equipment, etc.
The wireless communication networks are often referred to as Wireless Wide Area Network (WWAN). The internet service offered by such networks is often referred to as mobile broadband internet or Mobile Broadband (MB) and the WWANs are often referred to as mobile broadband networks. The terms WWAN and MB are used interchangeably herein. An example of a mobile broadband network may be based on the Long Term Evolution (LTE) from the 3rd Generation Partnership Project (3GPP). The LTE technology and its evolution are often referred to as fourth generation (4G) technologies. A client device may also use any of the previous generation technologies such as “2G”, “3G” from 3GPP and other standardization bodies. A client device and a network may also use future generation technologies for current and new services. A WWAN operator may deploy multiple Radio Access Technologies (RATs) such as 3GPP LTE, 3GPP Universal Mobile Telecommunications Service (UMTS), Global System for Mobile communication (GSM), Code Division Multiple Access (CDMA), Evolution Data Only/Evolution Data Optimized (EVDO), etc. Different client devices with different capabilities may connect to the WWAN using different suitable RATs for getting internet service. There may be one or more WWAN operators providing service in a particular geographic area. Each WWAN operator may use the same or different types of RATs. For providing end-to-end services, a WWAN many include, in addition to RATs, other network elements such as gateways and interfaces with other networks. Some client devices may have capability of supporting multiple Subscriber Identity Modules (SIMs) corresponding to different WWAN internet service providers. Some client devices with multiple SIMs may be able to get internet service from multiple WWANs simultaneously.
Typically, as shown in FIG. 1, a WWAN comprises one or more base stations. Other network devices may also be employed, such as a mobile switching center (not shown). As illustrated in FIG. 1, the communication path from the base station (BS) to the client device or mobile station (MS) is referred to herein as a downlink (DL) direction or downlink channel. The communication path from the client device to the base station is referred to herein as an uplink (UL) direction or uplink channel. In some wireless communication systems, the client device communicates with the BS in both the DL and UL directions. For instance, such communication is carried out in cellular communication systems. In other wireless communication systems, the client device communicates with the base stations in only one direction, usually the DL. Such DL communication may occur in applications such as paging. Typically in a wireless communication system, the client device and the base station may transmit information in blocks of data and such a block of data is referred herein as a “message.”
A base station to which a client device may be downlink synchronized and/or communicating at any given time is referred herein as the Serving Base Station (SBS). In some wireless communication systems the serving base station may be referred to as the serving cell. The base stations that are in the vicinity of the serving base station are called Neighbor Base Stations (NBS). Similarly, in some wireless communication systems a neighbor base station may be referred to as a neighbor cell.
A client device, after initially synchronizing with a cell, may switch to another cell depending on the signal conditions, network congestion, and other criteria. The process of switching from one cell to another cell by a client device is often referred to as handover (HO) or cell reselection. In some wireless communication systems handover is also referred to as handoff. Also in some wireless communication systems cell reselection is also referred to as idle mode handoff. An NBS, to which a client device may be switching over its communication from the current SBS, is herein referred to as Target Base Station (TBS). In some wireless communication systems, a target base station is normally referred to as a target cell. Sometimes, during a handover, the serving cell and the target cell may be the same and only the channel used for communication may be changed. Such a handover, in which the cell is not changed, is called as an intra-cell handover. The purpose of intra-cell handover may be that the new channel is better suited for communication than the previous channel within the same cell. Cell reselections or handovers amongst cells that use the same frequency are referred herein as intra-frequency cell reselection or handover. Cell reselections or handovers amongst cells that use different frequencies are referred herein as intra-frequency cell reselection or handover. A network may use different Radio Access Technologies (RATs) for providing various services. In a particular network, the cells of different RAT types may be overlapping or adjacent to each other. If a neighbor cell is using a RAT type that is different from the RAT type used by the serving cell, it is referred to as an inter-RAT neighbor cell.
The decision making process for handovers and cell reselections varies from one wireless communication system to another. However, the decisions are generally based on the signal conditions measurements by the client devices and reporting of those measurements to the wireless communication network by the client devices. The wireless communication network generally may influence and control the measurements and reporting process of the client device by providing parameters for the measurement and reporting process. The actual decision to perform handover may be made either by the wireless communication network or by the client device depending on the type of particular wireless communication system. On the other hand the cell reselection decisions in idle mode (i.e., when client device is not in active communication with the wireless communication network) may be generally performed autonomously by the client device. Both handovers and cell reselections may normally lead to change of cell from which the client device may access communication services. The difference between the handover procedure and cell reselection procedure may depend generally on whether a client device is engaged in an active communication with the wireless communication network. The measurements may include the Received Signal Strength Indicator (RRSI), Signal-to-Noise and Interference Ratio (SINR), the physical identities of one or more cells that may be visible or detectable by a client device, the difference between the timing of the current cell on which a client device may be camped and the timing of the neighbor cells. For example, in case of 3GPP LTE, the measurements may include Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Physical Cell Identity (PCI), etc.
In idle mode, a client device for the most part may turn off a majority of its circuitry to reduce power consumption. This is often referred to as “sleep” state, a sub-state within the idle mode. A client device may remain in a sleep state for a long duration and may wake up at the desired time window where it expects to receive the paging messages and certain SIBs. This alternating sequence of sleep and wake-up in idle mode is referred herein as Discontinuous Reception (DRX). The sleep and wake-up sequence may follow regular pattern and its period is often referred to as DRX cycle. The success rate for the incoming calls (e.g., mobile terminated voice calls and/or data calls) in a client device is directly related to the successful reception of paging messages. Normally, in idle mode, in addition to the reception of paging messages and SIB messages, a client device may continue to search and monitor neighbor cells. In connected mode, a client device may be actively engaged in communication with the network for data transfer in downlink, uplink, or both directions.
When a client device attempts to perform a network registration procedure to get service from a cell, it first decodes the system information broadcast in the cell. The client device may store such system information. The system information carries important information regarding the cell reselection criteria. Such information may include but not limited to the Tracking Area Identity (TAI), Public Land Mobile Network Identity (PLMN ID) which uniquely identifies a particular network operator, Closed Subscriber Group Identity (CSG ID), RAT type, neighbor cell frequencies, etc. This information may help to decide whether a cell is a “suitable cell” for the client device to avail all the services offered by it, or the cell is an “acceptable cell” where the client device may avail only limited services such as emergency calls. The client device may have to perform the network registration procedure to get service from the network and for the network to be able to page the client device for mobile terminated (incoming) calls. The network registration procedure may be typically performed by a client device with a particular cell. A group of cells in the geographic vicinity of each other may form a registration area. A registration area may be identified based on the system information of a cell. For example, the tracking area of a group of cells in a registration area may be the same.
Each base station in a wireless communication network may be identified by a unique identifier referred to herein as Cell Identity (CID). The CID of a base station may become known to a client device when it decodes SI from the base station. To avoid unnecessary updates from a client device and yet ensure the ability to reach a client device at any given time, the network may organize a group of cells into a “tracking area” and use a TAI to identify the various groups of cells. This is shown in FIG. 2 where four different tracking areas are illustrated. A cell may broadcast information about the tracking area it belongs to by including the TAI information in the system information. A client device may be required to inform the network when it begins to receive service from a cell that belongs to a tracking area that is different from the tracking area of the cells from which it was previously receiving service. The process of informing the network that the client device has begun receiving service from a cell that belongs to a new tracking area is referred herein as Tracking Area Update (TAU) procedure. With this method, a client device may perform TAU only when there is a change in TAI of the cell from which it is getting service. For example, in FIG. 2, when a client device reselects from the cell with CID=1003 to the cell with CID=1007 which has the same TAI, it may not perform TAU procedure. However, when the client device reselects from the cell with CID=1007 and TAI=200 to the cell with CID=1012 and TAI=201, it may perform TAU procedure.
Different client devices may be identified using their respective unique identities. For example, International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI), the Media Access Control (MAC) address, the Internet Protocol (IP) address may be used for the identity. Regardless of any particular identity used, it is generically referred herein as Client Device Identity (CDI).
As long as a client device is in the same registration area, the client device may not perform network registration procedure again except that a periodic network registration update procedure may need to be performed even if the client device continues to be stationary or move within the same registration area. If the client device moves to a cell which does not belong to the registration area in which the client device is registered, then the client device may perform network registration procedure to continue to access service from the network. Similarly, as long as a client device is in the same TAI, the client device may not perform TAU procedure again except that a periodic TAU procedure may need to be performed even if the client device continues to be stationary or move within the same TAI.
A client device may use internet service from one or more of the available internet service sources. A client device may access the internet service directly through one of the primary sources of internet service as mentioned earlier. Alternatively, a client device may access the internet service through a local network, which may perform distribution of the primary internet service to the users localized in a given area. Examples of such local networks include Local Area Network (LAN) using Ethernet, Wireless LAN (WLAN) commonly known as Wi-Fi, Bluetooth™, Zigbee or some other local area networking schemes. The wireless local networking schemes are collectively referred herein as Short Range Wireless Link (SRWL). The wire-line local networking schemes, such as Ethernet, are referred herein as Short Range Cabled Link (SRCL). Both the SRWL and SRCL together are referred to as Short Range Link (SRL). When a client device is in proximity of a location where an SRL access is available, it may access the internet service using the SRL.
The local area where WLAN service is available is often referred to as a Hotspot. The device that offers the WLAN service in a given local area is referred to as an Access Point (AP). In the present disclosure, the terms Hotspot AP or Hotspot are used interchangeably to refer to the device that offers the WLAN service in a given local area. As the variety of client devices has increased and the demand for MB service has increased, a device known as a mobile Hotspot is commonly used. A mobile Hotspot device includes both a modem for WWAN and a WLAN AP (Hotspot AP) to distribute the internet service to local client devices. FIG. 3 illustrates an example scenario of client devices accessing the internet 314 using the mobile Hotspot 302 which includes the WWAN modem 304 and WLAN Access Point 306. The client devices smartphone 308 and tablet 310 connect to the WLAN Access Point 306 over the WLAN SRWL 312. The WLAN Access Point 306 is connected to the WWAN modem 304 which is in turn connected to a WWAN 316 using the communication link 320. The client device smartphone 308 may maintain communication link 318 with the WWAN even when it is receiving internet service from mobile Hotspot 302. The client device tablet 310 which may not have WWAN modem maintains only the SRWL 312 with the mobile Hotspot 302.
FIG. 4 illustrates the block diagram of an example mobile Hotspot device. As shown in FIG. 4, for the chosen example, the WWAN modem and the WLAN AP may be connected to each other via one of the standard interfaces used in the industry such as Universal Serial Bus (USB), Secure Digital Input Output (SDIO), or proprietary interfaces. In another mobile Hotspot example, the WWAN modem and the WLAN AP may be an Integrated Circuit (IC) as shown in FIG. 5.
When a client device is connected to an SRWL such as the WLAN for internet service, it may continue to maintain its link with the WWAN for services other than internet service. This is shown by communication link 318 between smartphone 308 and WWAN 316. For example, a voice call or a video call to or from the phone number associated with the client device may be enabled through the WWAN while the internet service may be accessed through WLAN. The maintenance of the link with the WWAN may not necessarily require an active connection (a call or an internet service), but it may involve a number of procedures that a client device may need to perform. A client device may need to continue to receive paging messages from the WWAN in order to receive any incoming voice or video calls. A client device may need to perform measurements on SBS and NBSs as well as decode the SI from the SBS and some of the NBSs. A client device may need to perform TAU procedure with the WWAN whenever it reselects to a neighbor cell with a TAI different from a TAI of its current serving cell. A client device may need to perform registration procedure with the WWAN when it reselects to a cell in a different registration area or when a periodic registration update is required. Collectively, all the procedures performed by a client device in idle mode with WWAN are referred to as idle Radio Resource Management (RRM) procedures. In FIG. 3, the link 318 between the WWAN modem of a client device smartphone 308 and the WWAN 316 is maintained for the purposes mentioned above, even when the client device is getting internet service from the WLAN.